Correlation between DNA bases and the intensity of the Raman bands with SERS

Raman spectroscopy has become a popular tool for analyzing biological samples such as DNA. It allows us to access to the vibrational levels of molecules and thus to identify the chemical composition and to observe the structure of molecular systems.[1] In this work, we recorded the SERS spectra of DNA strands with different sequences and grafted at the surface of gold nanoparticles. Our objective is to study the correlation between the DNA sequences and its base composition and the intensity of Raman bands observed in SERS. To reach a high density of DNA on the surface of the gold nanoparticles, the DNA strands include a thiol group (SH) at their 5' end and are conjugated to gold nanoparticles using the freeze-thaw cycle method. SERS measurements are performed on dried drops deposited on a glass slide. We recorded 5 spectra for each sample using a 785nm excitation wavelength. We observed several bands that can be assigned to the different bases and to the phosphate backbone. For instance, the bands of ring breathing mode of adenine and the carbonic skeleton of the DNA are observable at 733cm-1 and 1029cm-1 respectively.[2] We then compare the relative intensity of the different bands such as the 733cm-1 or 1029cm-1 ones. We found that the relative intensity of the 733cm-1 band is correlated with the amount of adenine in the DNA sequence. This study provides a new approach for reliable quantification and analysis of genetic information associated with DNA molecule sequencing.